Gas cell for the optical analysis of gases

Abstract

A measuring cell for a gas analysis spectrometer has an inner chamber (23) for a sample gas to be analyzed and an inlet (21) and an outlet (22) which are connected thereto. A traversing optical path for a measuring beam (14) is formed in the inner chamber (23). The measuring cell is tubular, the inlet (21) and the outlet (22) are arranged at opposite ends, and the inner chamber (23) of the measuring cell has a cross-sectional shape that is monotonic over the length of the tube and which has an oval-shape at the start, which disappears toward the end. That special shape results in fast gas exchange and thus high dynamics, even with larger measuring cells, which have high sensitivity due to the long optical paths thereof. Two characteristics which until now appeared to be conflicting are thereby combined.

Description

[0001]This application is a continuation of Ser. No. 13 / 885,178, filed Jul. 18, 2013 as the national stage of PCT / EP2011 / 070462, filed on Nov. 18, 2011 and claims Paris convention from DE 10 2010 051 928.6, filed Nov. 19, 2010, the entire disclosures of which are hereby incorporated by reference.BACKGROUND OF THE INVENTION[0002]The invention concerns a measuring cell for a gas analysis spectrometer with an inner chamber for a gas to be analyzed, an inlet and an outlet, wherein a traversing optical path for a measuring beam is formed in the inner chamber.[0003]The optical analysis of gases is applied widely in various areas of technology. Special requirements are demanded by exhaust gas measurement applications for internal-combustion engines. Due to increasingly strict exhaust gas regulations, not only is a high level of sensitivity required to achieve a low detection threshold, but also a high time resolution to ensure a sufficiently good dynamic response of the measurement, in par...

AI Technical Summary

Benefits of technology

The invention is a measuring cell with a special shape that optimizes the formation of a vortex and allows for fast gas exchange without the need for secondary curls or other fluidic figures. The cell volume is designed to be larger than previous attempts in prior art, which improves its dynamic response and detectability. The invention achieves these improvements by a simple shaping of the measuring cell, unlike previous attempts that required small size or complicated shapes. The invention also provides favorable vortex formation and optimal flow-advantageous main vortex formation that stabilizes the flow and ensures the desired penetration of the entire inner chamber volume with the main vortex. The outlets for the exiting sample gas are preferably constituted with an axial component to optimize optical path generation and unimpended exit of the gas. The outlets are particularly well designed to achieve a good discharge characteristic from the inner chamber into the outlet of the sample gas.

Problems solved by technology

This results in a conflict of objectives between detection sensitivity and the time resolution of the system.

Increasing the volume of the measuring cell therefore has the disadvantage that, while other parameters remain constant, the time required to completely replace the gas increases, causing the time resolution and therefore the dynamic response to decrease correspondingly.

In such a measuring cell, however, relatively large “dead zones” are formed, which increase the exchange time and worsen the dynamic response.

The resulting time delay causes carryover (concentration carryover), which in turn results in a long response time of the measuring cell and therefore of the entire measuring system.

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